Improvements in or relating to a method and apparatus for detecting the presence of contaminants in a gaseous carrier.

摘要

The invention concerns the detection of cantaminant in a stream of gas. Previous methods have either been insufficiently sensitive or have been slow and needed skilled operatives. The present invention allows speedy operation with relatively unskilled operatives.
<??>A piezo electric crystal oscillator (1) is allowed to oscillate for a known period of time and the number of oscillations is counted. For a known time the crystal is exposed to contaminant, and is then allowed to oscillate again for the same period of time as before and the oscillations again counted. The difference in number of oscillations is a measure of the mass of contaminant deposited on the crystal (1). The period of oscillation of the first crystal is determined by a second matched crystal oscillator (2) in which the crystal is exposed to the same environment but not to contaminant.
<??>The apparatus has the advantage of being self-zeroing, and the exposed crystal (1) does not need cleaning after each use. The invention has special application to the testing of medical gases, for example oxygen and nitrous oxide.